Arrangements for the capacitive measurement of the level of fill of a substance in a container using a measuring electrode and an evaluation circuit have been known for a long time.
In such arrangements, the capacitance between the measuring electrode and the usually metallic container is evaluated. The capacitance depends essentially on the fill height of the fill substance in the container.
As a rule, the capacitance is ascertained by determining the reactance of the measuring arrangement. For this, an alternating voltage is produced, and the associated alternating electrical current, or its amplitude, is measured. There is a simple relationship involving the amplitude of the alternating voltage and the amplitude of the alternating current, also referred to as the amount of current, for obtaining reactance, and, from that, using the frequency, the capacitance can be calculated.